Semiconductor device with enhanced switching speed and method for manufacturing the same

Abstract

A method for manufacturing a semiconductor device according to the present invention has a step of forming a plurality of MOSFETs each having a channel of a first conductivity type in a stripe on the first major surface of a wafer; a step of implanting an impurity of a first conductivity type into the second major surface of the wafer, and performing a laser annealing treatment in a stripe leaving equidistant gaps, to form a buffer layer that has been activated in a stripe; a step of implanting an impurity of a second conductivity type into the second major surface of the substrate after forming the buffer layer, and performing a laser annealing treatment on the entire surface of the second major surface, to form a collector layer, and to activate the buffer layer; and a step of forming an emitter electrode on the first major surface, and forming a collector electrode on the second major surface.

1. A semiconductor device comprising:
 a plurality of MOSFETs each having a channel of a first conductivity type formed in a stripe on the first major surface of a wafer; 
 a buffer layer of a first conductivity type formed on the second major surface of said wafer, wherein highly activated portions and lowly activated portions are alternately formed in a stripe, an impurity concentration of the highly activated portions is the same as an impurity concentration of the lowly activated portions, an activation rate of impurities in the highly activated portions is higher than an activation rate of impurities in the lowly activated portions; 
 a collector layer of a second conductivity type formed on the second major surface side of said wafer than said buffer layer; 
 an emitter electrode formed on the first major surface of said wafer; and 
 a collector electrode formed on the second major surface of said wafer. 
 
   
   
     2. The semiconductor device according to  claim 1 , wherein
 the direction of the stripe of the highly activated portions and lowly activated portions in said buffer layer is made perpendicular to the direction of the stripe of said plurality of MOSFETs. 
 
   
   
     3. The semiconductor device according to  claim 1 , further comprising a guard ring formed on said first major surface in the circumference of the region for forming said plurality of MOSFETs wherein
 said highly activated portions are formed on the entire surface of the region in said buffer layer corresponding to the region for forming said guard ring.